1. Field of the Invention
The present invention relates to a golf ball, and more particularly, to the golf ball having an improved arrangement of dimples to be formed on the surface of the golf ball and a novel volume ratio between dimples corresponding to the regions thereof so as to improve the symmetricalness of the golf ball.
2. Description of the Related Arts
Normally, 300 to 550 dimples in number are formed on the surface of a golf ball. The principal role of dimples is to improve the aerodynamic characteristic thereof while the golf ball is flying, to optimize the trajectory, and to increase the carry or flying distance thereof.
In order to improve the aerodynamic characteristic of the golf ball, as disclosed in Oka et al., U.S. Pat. No. 4,813,677, it is preferable to form dimples densely on the surface thereof and reduce the number of great circle zones which intersect no dimples.
However, one great circle zone is inevitably formed on the surface of the golf ball. The golf ball is normally molded by a split metallic mold composed of semi-spherical upper and lower molds, a burr is formed at the junction of the molds, i.e. at a parting line between the upper and lower molds during the molding. Such burr is to be scraped off in a later processing by buffing to form a seam thereat, and therefore, the dimples can not be provided on the seam to facilitate buffing of the burr. In result, the golf ball has on its spherical surface a great circle zone which intersect no dimples even though dimples are densely formed thereon.
The great circle zone presents the aerodynamic characteristic clearly different from that of spherical surfaces of other golf ball having dimples densely formed thereon. That is, the great circle zone causes the following two problems. The first problem is the unsymmetricalness of the golf ball during its flight. The second problem is a putted golf ball does not roll straight.
It is preferable that the golf ball flies in the same trajectory wherever a golf club hits the golf ball. But the great circle zone differentiates the effect of dimples arranged in the vicinity of the great circle zone and the effect of dimples densely arranged in the vicinity of the poles from each other. Thus, the trajectory height in a seam hitting differs from that in a pole hitting. In a seam hitting, i.e., when the golf ball is struck in such a manner that the line connecting both poles serves as the rotational axis of a back-spin thereof, the portion where the circumferential speed of the rotary axis is the fastest coincides with the seam, thus undesirably lowering the trajectory height as compared with that when another line is set to be the rotary axis. The reason is that since, in the seam hitting, the circumference which is rotated fastest coincided with the parting line, the dimple effect of the golf ball on the whole is decreased to prevent the generation of the lift. The pole hitting means that the golf ball is struck in such a manner that a line perpendicular to the above-described rotational axis serves as the rotational axis of the back-spin thereof.
It is preferable that the golf ball follows along the same line on the green supposing that it is putted by a putter in the same manner or by the same force. But the great circle zone does not allow the golf ball to roll forward straight when it is putted by the putter in such a manner that the line connecting both poles thereof serves as the rotational axis of an over-spin. That is, as shown in FIG. 18, the parting line L of a golf ball 1 and portions in the vicinity thereof contact the green. The configuration of a dimple 2 positioned in the left of the seam L is different from that of the dimple 2 positioned in the right. Therefore, the extent of force applied to the golf ball from the left is different from that of force applied thereto from the right. Thus, the golf ball turns to the left or the right, thereby resulting in an unfavorable directivity, namely, an undesired rolling to the left or the right not along a targeted line. This is a trouble to golf players considering that many golf players putt the golf ball with the parting line L aligning with a putting line.
In order to overcome the previously described unsymmetricalness of the golf ball during its flights, namely the trajectory height in the seam hitting differs from that in the pole hitting, Yamada, U.S. Pat. No. 4,744,564 discloses the following technique. That is, the volumes of dimples arranged in the vicinity of the seam are larger than those of dimples arranged in the vicinity of the poles so as to improve the dimple effect in the vicinity of the seam, namely, to equalize trajectory height in the seam hitting to that in the pole hitting.
However, this art is incapable of solving the second problem, referred to previously, that a putted golf ball turns to the left or the right.